Researchers explore wireless charging of pacemakers, internal medical devices via wearable metasurface

Some of the organs in your body could malfunction quite a bit without ruining your life—but your heart isn't one of them: if it has problems, effective treatments are critical. Medical devices, such as pacemakers, can prevent a person's heartbeat from becoming too slow, or correct an irregular heartbeat. Unfortunately, the devices’ batteries don't last forever, meaning that surgery is eventually needed to replace either the device or its batteries.

But what if such surgeries weren’t necessary? What if a pacemaker's batteries and other internal medical devices could be charged wirelessly?

That's the idea being explored by a team of researchers at the University of Illinois Urbana-Champaign. Electrical and computer engineering PhD student Hanwei Wang, his advisor Yang Zhao, who is an assistant professor in ECE, Bioengineering, and the Holonyak Micro & Nanotechnology Laboratory, and ECE Assistant Professor Yun-Sheng Chen recently published a paper outlining a new solution for wireless device recharging. Entitled ”A wearable metasurface for high efficiency, free-positioning omnidirectional wireless power transfer,” it appeared on December 13, 2021 in the New Journal of Physics.

"What we did in this paper is we proposed a device that does not require any power, battery, or any connection. The device will capture the ambient, ubiquitous power in the environment, like the radio RF power, to charge the implanted medical devices so they can become self-sustained," said Wang. "It can work by itself and reshape the magnetic field distribution by forming resonance."

The most critical problem in wireless charging is the limited efficiency that requires precise alignment between the source and the device being charged. This issue is more critical for embedded medical devices than commercial products, where the medical implants are difficult to be aligned exactly with the source.

The team’s design solved this critical problem.

Their concept involves using electromagnetic metamaterials, an artificial material (or device) made from unique 3D patterns of sub-wavelength structures. The geometry and arrangement of these structures make metamaterials interact with electromagnetic fields and waves in ways not found in nature. As powerful as metamaterials are, the complexity of the 3D structures is the main challenge to realize such materials. 

In this instance, they created a metasurface, a thin sheet of metamaterials to build their device. They designed the metasurface to keep the exact functionality of the metamaterial, but largely release the difficulty in fabrication. Such devices can be made using a standard process that industries use to produce computer chips. The metasurface re-distributes the magnetic field to enhance wireless charging, regardless of the orientation of the targeted electronics. They showed they could wirelessly charge not just a single device, but multiple devices at a time, with the ability to rearrange the field direction to enhance the efficiency of charging between the various devices. Their new invention allows the wireless charging source to be away from the targeted device, greatly improving the convenience and making the wireless charging of embedded medical devices such as a pacemaker possible.

"People keep thinking about how to change the source to be able to charge a device more efficiently. Now we change the way how we receive the source to charge it efficiently," said Zhao.

They believe that to charge a medical device such as a pacemaker, a metasurface could be made, for example, in the form of a 10-cm by 10-cm patch with a thickness of roughly one millimeter. The patch could then be applied to a person's body or clothes to wirelessly charge a pacemaker within the person’s body. It wouldn't require its own battery to do so.

This isn't the team’s first work in this area. The concept of using a metasurface for wireless charging grew from earlier work on enhancing the magnetic field of MRI machines to focus on specific parts of the body, and thus shorten the amount of time a person would have to spend in the machine. They realized that both wireless power transfer and MRI require manipulation of the magnetic field, and they note that their approach could also have other applications, such as wireless charging of cell phones without docks, or remote charging of electric vehicles.

"The thing that interests me most is if I can bring some physics concepts like electromagnetics and metamaterials into the applications that can really benefit our lives," said Wang. "We really want to apply that electromagnetic knowledge into the sensor device and imaging technique that can benefit our lives instead of just as a theoretical study.”

The team is now working towards a metasurface device that can be first demonstrated in mice.

“There are so many problems in the medical community this physical concept can help,” said Zhao, “Such metasurfaces can miniaturize optics, improve imaging quality, enhance the sensitivity of molecular detection, and improve the efficiency of wireless charging. By designing each structure of the metasurfaces but not purely rely on periodicity, we can think of completely different ways to control electromagnetic fields.”